Hitherto, there has been proposed an automobile seat which is provided with a height adjusting device for adjusting a height of the automobile seat. Moreover, such a height adjusting device is applied to a slide-type seat for an automobile, which can be slid forward and rearward in the automobile (International Publication No. WO2004/094180A1, Japanese Patent Application Laid-Open No. 2000-108734, Japanese Patent Application Laid-Open No. 2000-127813, and Japanese Patent Application Laid-Open No. 2001-138789).
Referring now to FIG. 1, an automobile seat provided with the conventional height adjusting device will be discussed hereinafter in order to facilitate understanding of the present invention. The automobile seat includes a slide rail mechanism S which comprises a pair of spaced apart lower rail members R and a pair of spaced apart upper rail members A slidably supported to the lower rail members R (only one lower rail member R and only one upper rail member A are shown in FIG. 1). The upper rail members A have forward and rearward brackets 1a, 1b provided thereon so as to stand up from the upper rail members A. The height adjusting device includes a linkage base frame 15 which is provided between the forward and rearward brackets 1a, 1b and side frames 2 of a seat cushion of the seat (only one side frame 2 is shown in FIG. 1). More particularly, the linkage base frame 15 comprises forward linkage members 3 and rearward linkage members 4 (only one forward linkage member 3 and only one rearward linkage member 4 are shown in FIG. 1). The forward linkage members 3 are pivotally supported at lower end portions thereof to the forward brackets 1a by support pins 3a and supported at upper end portions thereof to the side frames 2 by support pins 3b, so that the forward linkage members 3 are bridged between the forward brackets 1a and the side frames 2. A connecting shaft 5 interconnects the forward linkage members 3. The rearward linkage members 4 are pivotally supported at lower end portions thereof to the rearward brackets 1b by support pins 4a and supported at intermediate portions thereof to the side frames 2 by support pins 4b, so that the rearward linkage members 4 are bridged between the rearward brackets 1b and the side frames 2. A connecting shaft 6 is connected to the support pins 4b, to thereby interconnect the rearward linkage members 4.
In order that the linkage base frame 15 is actuated, the height adjusting device further includes an operating knob 7 arranged outside one of the side frames 2 with a rotating shaft 7a thereof penetrating through the one of the side frames 2, a pinion gear 8 arranged inside the one of the side frames 2 and mounted on an inner end portion of the rotating shaft 7a, a sector gear 9 arranged inside the one of the side frames 2, rotatably supported, via a support pin 9a, to the one of the side frames 2 and meshed with the pinion gear 8, and a rod 10 coupled between the sector gear 9 and corresponding one of the rearward linkage members 4 by means of support pins 9b, 11. Moreover, a gear cover 12 for covering the pinion gear 8 and the sector gear 9 from an inward direction is mounted onto an inner surface of the side frame 2. The rotating shaft 7a of the operating knob 7, which supports the pinion gear 8, and the support pin 9a of the sector gear 9 are held by the side frame 2 and the gear cover 12.
In the automobile seat provided with the conventional height adjusting device, when the seat is in a lowermost position, the forward and rearward linkage members 3, 4 are inclined rearward. In this condition, when the operating knob 7 is manually operated so as to be rotated in a direction, the pinion gear 8 is rotated and the sector gear 9 is then rotated about the support pin 9a, whereby the rod 10 is pulled so as to be moved forward. The forward movement of the rod 10 causes the rearward linkage members 4 to be pivoted about the support pins 4a so as to stand up and causes the forward linkage members 3 to be pivoted about the support pins 3a so as to stand up, whereby the seat is lifted up, namely, the seat is adjusted to a high position. Re-adjusting of the height of the seat in the lowermost position can be performed by causing the operating knob 7 to be rotated in the reverse direction.
In the seat provided with the conventional height adjusting device, when the seat is lowered and arrives at the lowermost position, the side frames 2 of the seat are abutted against the upper rail members A on which the brackets 1a, 1b are provided, whereby the downward movement of the seat is stopped. Therefore, when an occupant on the seat intends to cause the seat to be excessively lowered and operates the operating knob 7, or when any excessive load is applied to the seat which has been in the lowermost position, the side frames 2 are strongly abutted against upper surfaces of the upper rail members A on which the brackets 1a, 1b are provided. As a result, portions of the side frames 2 and portions of the upper rail members A which are strongly abutted against each other are deformed and/or damaged. Particularly, when the side frames 2 are deformed, to thereby cause the sector gear 9 and/or the pinion gear 8 to become jolted, there is a possibility that the engagement between the sector gear 9 and the pinion gear 8 will become poor.
Moreover, in a case where the height adjusting device is applied to a slide-type automobile seat with a position sensor system, in which position sensors, electrical wirings thereof and/or the like (any automotive electronic parts and/or the like) are arranged on upper surfaces of upper rail members of a slide rail mechanism or arranged in the vicinity of the upper rail members, when the occupant on the seat operates the operating knob in such a manner that the seat is excessively lowered, or any excessive load is applied to the seat in a condition where the seat has been in a lowermost position, side frames of the seat are abutted against the position sensors, the electrical wirings and/or the like, to thereby cause them to be damaged.
Moreover, the height adjusting device comprises several parts including the forward and rearward linkage members 3, 4 which are supported to the side frames 2 of the seat cushion, and the operating knob 7, the pinion gear 8, the sector gear 9, and the rod 10 which are supported to the one of the side frames 2, so that the structures of the side frame and/or arrangement of the parts around the side frame is likely to become complicated. Particularly, a considerable load, such as a weight load of the seat itself and/or a weight load of the occupant on the seat, is applied to the support pins 3b, 4b supporting the forward and rearward linkage members 3, 4, and the support pin 9a of the sector gear 9, so that positional relationships among them with respect to the side frame are hard to be determined, and the structure of the height adjusting device is likely to become complicated.
Moreover, in the height adjusting device for the automobile seat, if the rigidity of the linkage base frame 15 is poor and a considerable load is applied to the linkage base frame 15, the forward and rearward linkage members 3, 4 and parts around them are made to flex, so that the seat is hard to be stably supported, and/or it is hard to carry out the adjusting of the height of the seat. Therefore, it is desired that good rigidity of the linkage base frame 15 is ensured. However, the forward linkage member 3 which is arranged in the vicinity of the parts including the operating knob 7, the pinion gear 8, the sector gear 9 and the rod 10 is required not to interfere with their operations, so that the arrangement and shape of the forward linkage member 3 is considerably limited and it is not easy to ensure the good rigidity of the linkage base frame 15.
Moreover, in the height adjusting device for the automobile seat, the entire weight load of the seat is applied to the forward and rearward linkage members 3, 4 and, in a condition where the occupant has sat on the seat, the weight load of the occupant is additionally applied to them. When the height of the seat is to be adjusted, lifting of the linkage base frame 15 must be performed against the total weight load by only operating the operating knob, so that a considerable force is required in order to operate the operating knob and, therefore, it is hard to operate the operating knob.
In order to overcome the above problem, there has been proposed a height adjusting device in which biasing means for biasing the linkage base frame in such a direction that the linkage base frame is swung up is employed and, therefore, the linkage base frame can be easily swung up (for example, Japanese Patent Application Laid-Open Nos. 2000-108734 and 2000-127813). However, in order that a biasing force which is enough for a load including the entire weight load of the seat and the weight load of the occupant can be obtained, large-sized biasing means must be employed. Moreover, in the height adjusting device disclosed in Japanese Patent Application Laid-Open No. 2000-108734, the size of the biasing means is reduced by employing an eccentric shaft. However, it is necessary to ensure a movement of the eccentric shaft. Therefore, there is a problem that the height adjusting device becomes large-sized and a lowermost position of the seat is inevitably set so as to become high.
Moreover, in the height adjusting device for the automobile seat, the pinion gear 8, the sector gear 9, and the rod 10 are arranged inside the one of the side frames 2, and one of the forward linkage members 3 is arranged adjacent them, so that they must be arranged in such a manner that their operations are not interfered with one another, their structures are likely to become complicated, and their operations are considerably restricted. Therefore, in order that they can be effectively and smoothly operated, the structure of the height adjusting device is likely to become complicated.